Python 如何使用 boto3 有条件地将项目插入到 dynamodb 表中
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How do I conditionally insert an item into a dynamodb table using boto3
提问by aychedee
If I have a table with a hash key of userId and a range key of productId how do I put an item into that table only if it doesn't already exist using boto3's dynamodb bindings?
如果我有一个带有 userId 哈希键和 productId 范围键的表，只有当它不存在使用 boto3 的 dynamodb 绑定时，我该如何将它放入该表中？
The normal call to put_item looks like this
对 put_item 的正常调用如下所示
table.put_item(Item={'userId': 1, 'productId': 2})
My call with a ConditionExpression looks like this:
我对 ConditionExpression 的调用如下所示：
table.put_item(
Item={'userId': 1, 'productId': 2},
ConditionExpression='userId <> :uid AND productId <> :pid',
ExpressionAttributeValues={':uid': 1, ':pid': 3}
)
But this raises a ConditionalCheckFailedException every time. Whether an item exists with the same productId or not.
但这每次都会引发 ConditionalCheckFailedException。是否存在具有相同 productId 的项目。
回答by jimjkelly
The documentation for this unfortunately isn't super clear. I needed to accomplish something similar, and here's what worked for me, using boto3:
不幸的是，这方面的文档不是很清楚。我需要完成类似的事情，这对我有用，使用 boto3：
try:
table.put_item(
Item={
'foo':1,
'bar':2,
},
ConditionExpression='attribute_not_exists(foo) AND attribute_not_exists(bar)'
)
except botocore.exceptions.ClientError as e:
# Ignore the ConditionalCheckFailedException, bubble up
# other exceptions.
if e.response['Error']['Code'] != 'ConditionalCheckFailedException':
raise
Similar to the other answer, the key is in the attribute_not_exists function, but it was unclear to me initially how to get that to work. After some experimentation, I was able to get it going with the above.
与其他答案类似，关键在 attribute_not_exists 函数中，但我最初不清楚如何让它工作。经过一些实验，我能够按照上述方法进行操作。
回答by Venkat.V.S
You dont need the sortkey( or range key) just the partition key or hash key is enough.
您不需要排序键（或范围键），只需分区键或散列键就足够了。
try:
table.put_item(
Item={
'foo':1,
'bar':2,
},
ConditionExpression='attribute_not_exists(foo)'
)
except botocore.exceptions.ClientError as e:
# Ignore the ConditionalCheckFailedException, bubble up
# other exceptions.
if e.response['Error']['Code'] != 'ConditionalCheckFailedException':
raise
回答by Eyal Ch
i think that you will get better documentation using client.put_item rather than table.put_item
我认为您会使用 client.put_item 而不是 table.put_item 获得更好的文档
from boto3 documentation:
来自 boto3文档：
To prevent a new item from replacing an existing item, use a conditional expression that contains the attribute_not_exists function with the name of the attribute being used as the partition key for the table. Since every record must contain that attribute, the attribute_not_exists function will only succeed if no matching item exists.
要防止新项目替换现有项目，请使用包含 attribute_not_exists 函数的条件表达式，该函数的名称用作表的分区键。由于每条记录都必须包含该属性，因此 attribute_not_exists 函数仅在不存在匹配项时才会成功。
ConditionExpression:
条件表达式：
ConditionExpression (string) -- A condition that must be satisfied in order for a conditional PutItem operation to succeed.
An expression can contain any of the following:
Functions: attribute_exists | attribute_not_exists | attribute_type | contains | begins_with | size These function names are case-sensitive.
ConditionExpression（字符串）——一个必须满足的条件，条件 PutItem 操作才能成功。
表达式可以包含以下任何内容：
函数：attribute_exists | 属性不存在 | 属性类型 | 包含 | 开始于 | size 这些函数名称区分大小写。
i am using dynamodb2 overwrite parameteron item.save()
我使用dynamodb2覆盖参数上item.save()
